High pressure split die and associated methods

ABSTRACT

An improved high pressure apparatus can include a plurality of complementary die segments. The die segments can have inner surfaces which are shaped to form a die chamber upon assembly of the die segments. A pair of anvils can be oriented such that an anvil is at each end of the die chamber. To prevent the die segments from being forced apart during movement of the anvils, force members can be connected to the die segments. The force members can apply discrete forces to the die segments sufficient to retain the die segments in substantially fixed positions relative to each other during application of force by the pair of anvils. Using such a high pressure apparatus can achieve pressures as high as 10 GPa with improved useful die life and larger reaction volumes.

FIELD OF THE INVENTION

The present invention relates generally to devices used in high pressureapparatuses capable of ultrahigh pressures above several GPa. Such highpressure devices can be used for high pressure high temperature (HPHT)growth of diamond and/or CBN and for a variety of other purposes.Accordingly, the present invention involves the fields of chemistry,metallurgy, materials science, and high pressure technology.

BACKGROUND OF THE INVENTION

Apparatuses for achieving high pressures have been known for over a halfcentury. Typical ultrahigh pressure apparatuses include piston-cylinderpresses, cubic presses, tetrahedral presses, belt presses, girdlepresses, and the like. Several of these apparatuses are capable ofachieving ultrahigh pressures from about 4 GPa to about 7 GPa.

High pressure apparatuses are commonly used to synthesize diamond andcubic boron nitride (cBN), commonly known as superabrasives. In 2003,high pressure apparatuses provided a worldwide production of diamondsuperabrasives of about 600 tons, while about 200 tons of cBNsuperabrasives were produced. Generally, raw materials can be formedinto a high pressure assembly and then placed in the high pressureapparatus. Under high pressure and typically high temperature, the rawmaterials form the desired product. More specifically, graphite ordiamond can be used as a raw material in diamond synthesis, whilehexagonal boron nitride (hBN) can be used in cBN synthesis. The rawmaterial can then be mixed or contacted with a catalyst material.Diamond synthesis catalysts such as Fe, Ni, Co, and alloys thereof arecommonly used. Alkalis, alkali earth metals, or compounds of thesematerials can be used as the catalyst material in cBN synthesis. The rawmaterials and catalyst material can then be placed in a high pressureapparatus wherein the pressure is raised to an ultrahigh pressure, e.g.,5.5 GPa. An electrical current can then be used to heat the catalystmaterial sufficient to melt the catalyst material, e.g., typically about1300° C. Under such conditions, the raw material can dissolve into thecatalyst and then precipitate out in a crystalline form as eitherdiamond or cBN.

Unfortunately, currently known high pressure apparatuses and associatedmethods have expensive parts with limited useful life and limitedavailable reaction volumes. For example, a typical belt apparatusincludes an inner die which is shaped like a belt or doughnut, andconcentric metal rings formed around the inner die as support. Earlyexamples of belt apparatuses are described in U.S. Pat. Nos. 2,947,610and 3,031,269, which are incorporated herein by reference. A pair ofanvils is shaped to fit in the ends of the die opening. As such, theprimary compression source is the pair of anvils which essentiallyshorten the length of the reaction volume and thus increase the pressureon the material placed therein. Because of the use of a die, thebelt-type apparatuses may achieve ultrahigh pressures in a relativelylarger reaction volume than typical cubic and tetrahedral presses whichutilize retractable anvils without a die. Unfortunately, the die istypically formed of cemented tungsten carbide and concentric metal ringswhich are extremely difficult to make and involve considerable expense.Specifically, the die and concentric rings are assembled with highlyprecise interference fittings. Further, it is difficult to sinter alarge die with high uniformity which can often result in localized areaswhich are structurally weaker. In addition, the die material istypically metal carbide, e.g., tungsten carbide, which has a very highcompressive strength but relatively low tensile strength. As a result,these expensive dies frequently crack and fail due to extremely highhoop tension that develops around the circumference of the die as thedie and concentric rings expand during advance of the pair of anvils.

Other methods for achieving ultrahigh pressures include cubic andtetrahedral presses which utilize multiple advancing anvils to press asample. One such device is described in U.S. Pat. No. 3,159,876, whichis incorporated herein by reference. Cubic presses and belt-typeapparatuses can be used for diamond synthesis. However, the reactionvolumes of cubic presses are somewhat smaller than belt-typeapparatuses.

Therefore, apparatuses and methods which overcome the above difficultieswould be a significant advancement in the area of high pressure devices.

SUMMARY OF THE INVENTION

It has been recognized by the inventor that it would be advantageous todevelop a device which allows for larger production throughput,decreased production costs, and has lengthened useful die lives.

In one aspect, the present invention resolves the problems set forthabove by providing a high pressure apparatus including a plurality ofcomplementary die segments. The die segments can have inner surfaceswhich are shaped to form a die chamber upon assembly of the diesegments. A pair of anvils can be oriented such that an anvil is at eachend of the die chamber. The anvils can be oriented to apply force to thedie chamber substantially along the vertical axis of the chamber.Typically, the anvils are moved towards each other in order to shortenthe die chamber. To prevent the die segments from being forced apart bythe movement of the anvils, force members can be connected to the diesegments. The force members can apply discrete forces to the diesegments sufficient to retain the die segments in substantially fixedpositions relative to each other during application of force by the pairof anvils.

In one detailed aspect of the present invention, the die chamber canhave a wide variety of shapes. For example, the die chamber can have acentral volume having a tapered region at each end of the centralvolume. The central volume can be cylindrical, rectangular, or the like.The tapered regions can be gradually tapered or can be flat tapersoutward.

In another detailed aspect of the present invention, the die chamber canbe formed from a number of die segments. In one aspect, the highpressure apparatus can include from two to ten complementary diesegments. In two currently preferred embodiments the high pressureapparatus can have two to four complementary die segments.

In an additional aspect of the present invention, the die segments canhave outer surfaces which are attached to support members. The supportmember can also be connected to the force members which help to retainthe die segments together.

In yet another aspect of the present invention, the force members can bepairs of platen in a uniaxial press.

In still another aspect of the present invention, the support memberscan have an outer surface which is inwardly contoured to form a profile.The contoured surface of the support members can reduce tensile stressin the die segment.

In another aspect of the present invention, the support members and diesegments can have contact surfaces which are contoured to controlpressure distribution along the contact surfaces. Similarly, gasketmaterials can be contoured to correspond to the contours of the contactsurfaces.

In accordance with the present invention, a method of applying highpressures to a high pressure assembly can include assembling a pluralityof die segments to form a die chamber capable of holding the highpressure assembly. Force can then be applied to the high pressureassembly sufficient to provide high pressures within the reactionvolume. During application of force, the die segments can be retained insubstantially fixed positions relative to each other using a pluralityof discrete forces. Typically, the discrete forces can intersect at acommon point and act in a common plane substantially perpendicular tothe chamber axis. Alternatively, the die segments can be retained oraligned using tie rods. Such tie rods can be connected to correspondingsupport members.

The methods of the present invention can provide ultrahigh pressures inthe reaction volume. In one detailed aspect of the present invention,ultrahigh pressures from about 2 GPa to about 6 GPa can be maintainedfor a predetermined time. Typically, pressures can be maintained forseveral seconds to over 24 hours.

There has thus been outlined, rather broadly, various features of theinvention so that the detailed description thereof that follows may bebetter understood, and so that the present contribution to the art maybe better appreciated. Other features of the present invention willbecome more clear from the following detailed description of theinvention, taken with the accompanying claims, or may be learned by thepractice of the invention.

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a high pressure apparatus inaccordance with an embodiment of the present invention;

FIG. 2A is a perspective view of two die segments and correspondingsupport members in accordance with an embodiment of the presentinvention;

FIG. 2B is a perspective view of the die segments of FIG. 2A assembledto form a die chamber;

FIG. 3A is a perspective view of four die segments and correspondingsupport members in accordance with an embodiment of the presentinvention;

FIG. 3B is a perspective view of the die segments of FIG. 3A assembledto form a die chamber;

FIG. 4A is a perspective view of four die segments in accordance with anembodiment of the present invention;

FIG. 4B is a perspective view of the die segments of FIG. 4A assembledto form a die chamber;

FIG. 5A is a perspective view of two die segments and correspondingsupport members in accordance with another embodiment of the presentinvention;

FIG. 5B is a perspective view of the die segments of FIG. 5A assembledto form a die chamber;

FIG. 6 is a top view of four die segments mounted on two support membersin accordance with an embodiment of the present invention;

FIG. 7 is a side view of an axial press having two die segments andcorresponding support members mounted therein;

FIG. 8 is a top view of a contoured support member in accordance with anembodiment of the present invention; and

FIG. 9 is a top view of a portion of a support member and die segmenthaving a contoured contact surface in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features, process steps, and materialsillustrated herein, and additional applications of the principles of theinventions as illustrated herein, which would occur to one skilled inthe relevant art and having possession of this disclosure, are to beconsidered within the scope of the invention. It should also beunderstood that terminology employed herein is used for the purpose ofdescribing particular embodiments only and is not intended to belimiting.

A. Definitions

In describing and claiming the present invention, the followingterminology will be used.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a die segment” includes reference to one or more of such materials, andreference to “an axial press” includes reference to one or more of suchpresses.

As used herein, “anvils” refers to any solid mass capable of at leastpartially entering the die chamber to increase pressure within thereaction volume. Those skilled in the art will recognize various shapesand materials used for such anvils. Typically, the anvils can have afrustoconical shape.

As used herein, “complementary” when used with respect to die segments,refers to parts which fit together to form a specified reaction volumeconfiguration. The die segments “complement” each other by being shapedand configured to be held together under high pressures with minimal orno space between contact surfaces and to form an open die chamber.Frequently, complementary die segments can be configured to allowplacement of a gasket or other material between contact surfaces toimprove sealing of the reaction volume.

As used herein, “discrete force” refers to a force vector, which has anidentifiable source and is associated with a single force vector, asopposed to a summation of somewhat random forces acting on a body, e.g.,a gas or liquid surrounding a body.

As used herein, “reaction volume” refers to at least a portion of thedie chamber in which conditions can be maintained at a high pressuresufficient for useful testing and/or growth of materials which areplaced therein, e.g. usually the reaction volume can include a charge ofraw material and catalyst for formation of superabrasive. The reactionvolume can be formed within a high pressure assembly placed at leastpartially within the die chamber.

As used herein, “high pressure assembly” refers to an assembly ofmaterials which are to be subjected to high pressure. Most often, thesematerials include the reaction volume at least partially surrounded by apressure medium and/or gasket assembly. However, those skilled in theart will recognize that the high pressure assembly can be formed ofalmost any material which can then be subjected to high pressure forsuch purposes as chemical reactions, crystalline growth, high pressureproperty measurements, and the like. A wide variety of high pressureassemblies is known and can be used in the present invention. Such highpressure assemblies can also include inert gaskets, separators, or othermaterials which improve HPHT conditions.

As used herein, “high pressure” refers to pressures above about 1 MPaand preferably above about 200 MPa.

As used herein, “ultrahigh pressure” refers to pressures from about 1GPa to about 15 GPa, and preferably from about 4 GPa to about 7 GPa.

As used herein, “alloy” refers to a solid or liquid mixture of a metalwith a second material, said second material may be a non-metal, such ascarbon, a metal, or an alloy which enhances or improves the propertiesof the metal.

As used herein, “seeds” refer to particles of either natural orsynthetic diamond, super hard crystalline, or polycrystalline substance,or mixture of substances and include but are not limited to diamond,polycrystalline diamond (PCD), cubic boron nitride, SiC, and the like.Diamond seeds are used as a starting material for growing larger diamondcrystals and help to avoid random nucleation and growth of diamond.Particularly, seeds can be used to produce useful superabrasiveparticles.

As used herein, “superabrasive” refers to particles of diamond or cBN,including sintered polycrystalline forms of diamond and cBN.

As used herein, “precursor” refers to an assembly of diamond seeds,particulate catalyst layer, and a carbon source layer. A precursordescribes such an assembly prior to the diamond growth process, i.e. a“green body.”

As used herein, “inclusion” refers to formation of carbon depositsinstead of diamond at the interface between a growth surface of thediamond and the surrounding material. Inclusions are most often formedby the presence of substantial amounts of carbon at the growth surfaceof the diamond and/or inadequate control of temperature and pressureconditions during HPHT growth.

As used herein, “euhedral” means idiomorphic, or having an unalterednatural shape containing natural crystallographic faces.

As used herein, “substantially free of” or the like refers to the lackof an identified element or agent in a composition. Particularly,elements that are identified as being “substantially free of” are eithercompletely absent from the composition, or are included only in amountswhich are small enough so as to have no measurable effect on thecomposition.

Concentrations, amounts, and other numerical data may be presentedherein in a range format. It is to be understood that such range formatis used merely for convenience and brevity and should be interpretedflexibly to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited.

For example, a numerical range of about 1 to about 4.5 should beinterpreted to include not only the explicitly recited limits of 1 toabout 4.5, but also to include individual numerals such as 2, 3, 4, andsub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies toranges reciting only one numerical value, such as “less than about 4.5,”which should be interpreted to include all of the above-recited valuesand ranges. Further, such an interpretation should apply regardless ofthe breadth of the range or the characteristic being described.

B. The Invention

Reference will now be made to the drawings in which the various elementsof the present invention will be given numeral designations and in whichthe invention will be discussed. It is to be understood that thefollowing description is only exemplary of the principles of the presentinvention, and should not be viewed as narrowing the appended claims.

In accordance with the present invention, a high pressure apparatus caninclude a plurality of complementary die segments. The die segments ofthe present invention can be assembled to form a die chamber. The diechamber can be at least partially filled with a high pressure assemblycontaining materials to be subjected to high pressures. A pair of anvilscan be oriented such that an anvil is at each end of the die chamber.The anvils can then be moved towards each other to compress the highpressure assembly and apply force thereto. Additionally, a plurality offorce members can be operatively connected to the plurality of diesegments to retain the die segments in substantially fixed positionsrelative to each other during application of force by the pair ofanvils. One advantage to this configuration is that the die segments donot experience the same hoop tension around the die circumference as astandard single piece belt die.

Referring now to FIG. 1, a high pressure apparatus, shown generally at10, can include a plurality of complementary die segments 12 and 14.Each die segment can have an inner surface 16 and an outer surface 18.The die segments can be configured to be assembled to form a die havinga die chamber 20 capable of holding a high pressure assembly. The diechamber 20 can have a chamber axis 26 substantially along the center ofthe die chamber.

The die chamber 20 can be formed in a wide variety of shapes. FIG. 1illustrates a die chamber having a cylindrical portion having ends whichare tapered outward. The tapered portions are shown as taperinggradually to form a curved surface outward; however the tapered portionscan be also be flat as shown in FIGS. 2A and 4A. Alternatively, the diechamber can also be a straight cylinder without a tapered portion. Ofcourse, the die chamber can also have a shape which does not have acylindrical portion, wherein the tapered portions at either end comprisethe entire die chamber volume similar to a typical belt die. Typically,in this embodiment, the die chamber has a length which is from about 0.5to about 10 times the minimum chamber diameter. Regardless of the diechamber configuration, the die chamber can have a length of from about0.5 to about 15 times the minimum chamber diameter. In some embodiments,the die chamber can have a length of from about 1 to about 10 times theminimum chamber diameter. In an additional aspect of the presentinvention, the die chamber can have a reaction volume from about 1 cm³to about 1000 cm³, and preferably from about 10 cm³ to about 500 cm³.

Other die chamber configurations can also be used and are consideredwithin the scope of the present invention. In one aspect, the diechamber can have an interior surface which is substantially continuoussuch that when the die segments are assembled a single chamber extendsthrough the assembled die segments. Preferably, the die segments can beshaped such that adjacent surfaces are flush and have substantially nospace between them when assembled.

The inner surfaces of the plurality of die segments can be configured toform a die chamber having a predetermined cross-section. Specifically,the inner surfaces can be, but are not limited to, arcuate, flat, orcontoured surfaces. For example, when assembled, arcuate inner surfacescan form a die chamber having a circular cross-section. Similarly, whenassembled, flat inner surfaces can form a die chamber having triangle,square, pentagon, and the like cross-sections, depending on the numberof die segments.

In accordance with the present invention, the number of complementarydie segments can vary from two to any practical number. In one aspect,the high pressure apparatus of the present invention can include fromtwo to ten complementary die segments. As the number of die segmentsincreases, the relative size of each segment decreases. As a result,each die segment can be sintered having a higher degree of homogeneityand fewer localized structural weaknesses than a single die or largerdie segments. However, a greater number of die segments can alsoincrease complexity and maintenance costs of the apparatus, as describedin more detail below in connection with increased numbers and complexityof support members and presses. Typically, the number of die segmentscan be from two to four. In one detailed aspect, the high pressureapparatus can include two complementary die segments. In anotherdetailed aspect, the high pressure apparatus can include fourcomplementary die segments.

The die segments can be formed of any hard material having a highcompressive strength. Examples of suitable hard material for forming diesegments of the present invention can include, but are not limited to,cemented tungsten carbide, alumina, silicon nitride, zirconium dioxide,hardened steel, super alloys, i.e. cobalt, nickel, and iron-basedalloys, and the like. In a preferred embodiment, the die segments can beformed of cemented tungsten carbide. Those of ordinary skill in the artwill recognize other materials that may be particularly suited to suchhigh pressure devices.

Referring again to FIG. 1, the outer surface 18 can be configured toattach to respective support members 21 and 23. The outer surface can beany configuration such as flat or contoured; however typically the outersurface can be flat. The support members are optional in the highpressure apparatus of the present invention. However, it is oftenpreferable to provide support members to protect and reinforce the moreexpensive die segments. Typically, each die segment can have acorresponding support member. Alternatively, two or more die segmentscan be attached to a single support member. The support members can beformed of any hard metal. Non-limiting examples of suitable hard metalsinclude steel, hardened steel, metal carbides, ceramics, and alloys orcomposites thereof. Typically, the support members can be hardenedsteel. The die segments of FIG. 1 can be retained in substantially fixedpositions relative to each other via discrete forces 17 and 19. Mostoften, the die segments and support members can be separated by a thingasket material, e.g., pyrophillite or talc. The gasket material canprovide improved sealing between surfaces and helps to avoid localpressure spikes due to direct contact of two hard materials.

FIGS. 2A through 7 illustrate a few potential configurations forsegmented dies of the present invention. FIG. 2A shows a set of twocomplementary die segments 22 and 24, each engaged with a separatesupport member 21 and 23, respectively. The die segments can beassembled as shown in FIG. 2B to form die chamber 20 a. The die chambershown in FIG. 2B has a cylindrical portion and flat tapered portions ateach end of the cylindrical portion. Forces 27 and 29 can be applied tothe support members to retain the die segments together. An optionalgasket 25 can also be included between contacting surfaces of the diesegments and support members. The gasket can provide a seal betweensurfaces, as well as to electrically and/or thermally insulate.Typically, the gasket can be formed of known materials such as, but notlimited to, talc, pyrophillite, and the like. Additional materials suchas quartz and zirconia can be added to adjust various mechanical and/orthermal properties of the gasket.

FIG. 3A shows a set of four complementary die segments 32, 34, 36, and38, each engaged with a separate support member 31, 33, 35, and 37,respectively. The die segments can be assembled as shown in FIG. 3B toform die chamber 20 b. The die chamber shown in FIG. 3B has acylindrical portion and flat tapered portions at each end of thecylindrical portion. Forces can be applied to each of the four supportmembers to retain the die segments together. An optional gasket 25 a canalso be included between contacting surfaces of the die segments andsupport members. Additionally, optional gasket 25 b can be placed in thedie chamber, as is well known in the art.

FIG. 4A shows a set of four complementary die segments 42, 44, 46, and48 having no attached support members. As such, in some aspects of thepresent invention, the die segment may be used without a support member,or the die segment and support member can be a single integral piece.The die segments can be assembled as shown in FIG. 4B to form diechamber 20 c. The die chamber shown in FIG. 4B has a rectangular volumeand flat tapered portions at each end of the rectangular volume. Forcescan be applied to each of the four die segments to bring them together,and retain them in place when the anvils are used to apply pressurealong the chamber axis of the die chamber. An optional gasket 25 c canalso be included between contacting surfaces and between surfaces of thedie chamber and the high pressure assembly.

FIG. 5A shows a set of two complementary die segments 51 and 52, eachsurrounded by arcuate support members 53 through 58, respectively. Thedie segments can be assembled as shown in FIG. 5B to form die chamber 20d. The die chamber shown in FIG. 5B has a cylindrical portion and flattapered portions at each end of the cylindrical portion having a smallertaper angle than that of FIG. 2A. Forces can be applied to each of thesupport members to retain the die segments together. An optional gasket25 d can also be included between contacting surfaces of the diesegments and support members. Additionally, optional sleeves 59 and 60can be placed between the die segments 51 and 52 and support members 53and 56, respectively.

Similarly, a set of three complementary die segments can each beattached to a separate support member. The die segments can be assembledto form a die chamber. The die chamber can be shaped as in theconfigurations discussed herein. Forces can be applied to each of thethree support members to retain the die segments together. An optionalgasket can also be included between contacting surfaces of the diesegments and support members. Additionally, an optional gasket can beplaced in the die chamber, as is well known in the art.

FIG. 6 illustrates the four die segments and corresponding supportmembers of FIGS. 3A and 3B attached to two secondary support members 68and 70.

The above discussion has focused primarily on die segments wherein thedie segments are split along surfaces which are substantially parallelto the chamber axis along the center of the die chamber. However, in anadditional aspect of the present invention, the die segments can besplit in almost any configuration. For example, the die segments can besplit along a plane which is perpendicular to the chamber axis. Diesegments which split the die chamber perpendicular to the chamber axiscan allow for increased die chamber lengths and thus increased highpressure reaction volumes. In addition, perpendicular splits can improveaccess to the reaction volume during assembly, cleaning of the device,or replacement of failed die segments. Further, the perpendicular splitcan also allow for convenient insertion of thermocouples for temperaturemonitoring. As mentioned above, partitioning of the split die alsoreduces die segment production costs by allowing for smaller sinteringmasses and reduced non-homogeneous sintering.

Referring again to FIG. 1, a pair of anvils 70 and 72 can be orientedsuch that an anvil is at each end of the die chamber 20. The anvils canbe configured to apply pressing forces 13 and 15 substantially along thechamber axis through movement of the anvils towards one another toshorten the die volume. Most often, a high pressure assembly can beplaced in the die chamber such that the reaction volume is subjected tohigh pressure during application of force from the anvils. High pressureassemblies can contain a material to be subjected to high pressure suchas diamond seeds, graphite, catalysts, CBN seeds, hexagonal boronnitride, and the like. Typically, the high pressure assembly can includemetal braze coatings, gasket materials, graphite heating tubes,resistors, and the like. Those skilled in the art will recognizeadditional high pressure assembly compositions and configurations whichare useful for reaction and or experimentation at high pressures.

Anvils 70 and 72 are shown as masses having frustoconical portions whichare shaped to fit into the ends of the die chamber 20. In connectionwith the present invention, suitable anvil shapes can also include,without limitation, frustopyramidal, piston, and the like. For example,frustopyramidal anvils can be useful for use with die chambers such asdie chamber 20 c shown in FIG. 4B.

As the anvils advance, the materials placed in the die chamber have atendency to expand radially outward against the die segments. In orderto prevent movement of the die segments outward, a plurality of forcemembers can be operatively connected to the plurality of die segments.The force members can be configured to apply a plurality of discreteforces to the die segments, in some cases through the support members.The discrete forces should be sufficient to retain the plurality of diesegments in substantially fixed positions relative to each other duringapplication of force by the pair of anvils. Some minimal movement of diesegments can be permissible; however significant movement can allow forexcess material to be forced into spaces between die segments. Moreimportantly, if the die segments are allowed to move significantly, thenthe pressure within the reaction volume is reduced. Typically, theanvils have a limited distance which they can enter the die chamber, ascan be seen in FIG. 1. Thus, when the die segments are allowed to move,the maximum achievable pressure is significantly reduced.

In accordance with the present invention, the force members can be anydevice or mechanism capable of applying force sufficient to retain thedie segments in substantially fixed positions. Several non-limitingexamples of suitable force members include uniaxial presses, hydraulicpistons, and the like. Hydraulic pistons and rams similar to those usedin tetrahedral and cubic presses can also be used in the high pressureapparatus of the present invention. Alternatively, the force members caninclude tie rods and hydraulic pistons similar to those used in astandard cubic press. In one specific embodiment shown in FIG. 7, theforce members can be pairs of platen 72 in a uniaxial press 74. Diesegments 76 and 78 are held in arcuate support members 80 and 82,respectively. Support members 80 and 82 are also held in additionalsupport members 84 and 86, respectively. The die segments are shown in aseparated position. In this position, the die segments and/or supportmembers can be easily replaced or adjusted. Further, subsequent toapplication of high pressure retraction of the die segments to aseparated position can make removal of the high pressure assembly easierthan with standard belt dies. In one aspect, wherein four die segmentsare attached to four corresponding support members, two uniaxial pressescan be used to retain the four die segments in substantially fixedpositions. The segmented force and associated support members of thepresent invention can be advantageous in that removal of die segmentsand opening of the die chamber subsequent to application of highpressure is readily accomplished.

The die segments 76 and 78 can be assembled to form a die chamber byengaging the pair of platen 72 using the uniaxial press 74. As the diesegments move towards one another, optional guide pins 88 and 90 canensure that the die segments are correctly oriented and can help toprevent lateral sliding during application of high pressure.

Typically, the chamber axis of the die chamber 20 can be vertical asshown in FIG. 1. However, in some alternative embodiments of the presentinvention the chamber axis can be oriented horizontally prior toapplication of force by the anvils. Depending on the composition of thehigh pressure assembly, a horizontal orientation can help to reduceproblems associated with differences in density and temperaturegradients during diamond synthesis. For example, during synthesis ofdiamond, the catalyst is substantially molten such that lower densitydiamond (3.5 g/cm³) tends to float on the more dense molten catalyst(density greater than 8 g/cm³). Moreover, the molten catalyst may flowupward via convection, if the lower portion of the molten catalyst is ata higher temperature than an upper portion. Such flow of molten catalystor diamond is not desirable, e.g, under the temperature gradient methodof diamond synthesis, convection can increase diffusion of carbon solutesufficient to disturb the growth rate of the seeded diamond resulting innon-homogeneous crystal formation and defects. Thus, one aspect of thepresent invention can include orienting the chamber axis substantiallyperpendicular to gravity in order to eliminate or substantially reducesuch effects.

Regardless of the force members used, the force members can beconfigured to apply discrete forces to the die segments, either directlyor via corresponding support members. In one aspect of the presentinvention, the discrete forces can intersect at a common point and actin a common plane substantially perpendicular to the chamber axis.Typically, the common point is along the chamber axis in order toprevent sliding or offsetting of the die segments with respect to oneanother.

Referring to FIG. 2B, the two die segments 22 and 24 are retainedtogether using discrete forces 27 and 29. Discrete forces 27 and 29 canbe applied about 180° apart and about 90° to an interface plane definedby the interface of the die segments, corresponding generally to gasket25. Similarly, FIG. 3B illustrates three die segments 62, 64, and 66being retained together using discrete forces 27, 28, and 29,respectively. Discrete forces 92, 94, and 96 can act in a common planeabout 120° apart and about 60° to the die segment interfaces. FIG. 3Billustrates four die segments 32, 34, 36, and 38 being retained bydiscrete forces 102, 104, 106, and 108, respectively. Discrete forces102, 104, 106, and 108 can act in a common plane about 90° apart andabout 45° to the die segment interfaces.

The advancing anvils act as a wedge to push the die segments apart. As aresult, the amount of force required to retain the die segments togetheris typically greater than the force applied by the anvils. Therefore,the discrete forces combined can preferably be greater than the combinedpressure from the anvils. In one detailed aspect of the presentinvention, as the pair of anvils advances, pressure is placed on thehigh pressure assembly such that force is applied radially outwardagainst the die segments. As a result, the combined discrete forcesrequired in order to retain the die segments can be greater than thepressure in the high pressure assembly. In addition, a typical die hasan inner surface area larger than the anvils; consequently, the force(i.e. pressure times area) required to retain the die segments togetheris much larger than the force required to advance the anvils. Typically,anvils can provide a pressing force of from about 100 metric tons toabout 10,000 metric tons, although forces outside this range can be usedwhich are sufficient to achieve the desired pressures.

In accordance with the above principles, the high pressure apparatus ofthe present invention can produce high pressures within the die chamber.High pressures of over about 2 MPa can be easily achieved. In oneaspect, the combined pressing forces are sufficient to provide ultrahighpressures. In one detailed aspect, the ultrahigh pressures can be fromabout 1 GPa to about 10 GPa, and preferably from about 2 GPa to about 7GPa, and most preferably from about 4 to about 6 GPa.

In yet another detailed aspect of the present invention, the supportmembers can be shaped to reduce tensile stress in a corresponding diesegment. Application of force to support members such as those shown inFIG. 2B can cause premature failure of the die segments. Specifically,upon applying force to the support members 21 and 23 the die segmentscan experience a high tensile stress along a region of the inner surfaceof the die chamber. This tensile stress tends to cause cracking of thedie segments, wherein cracks have a genesis at the inner surface whichthen grows toward the outer surface. FIG. 8 illustrates a support member110 having a single arcuate die segment 112. The support member has anouter surface 114 which is opposite the die segments. The outer surfacecan be preferably inwardly contoured to form a profile configured toreduce tensile stress in the die segment. Optionally, a correspondingforce member can be inwardly contoured to form a similar profile whichdecreases tensile stress in the die segment during application highpressure. The inward contour can be a slight inward concavity such asthat shown in FIG. 8; however the inward contour can also be formed as abeveled surface having substantially flat surfaces which slope inwardand meet at a maximum deviation, L_(D). Other inward contours can alsobe used which decrease tensile stress at the inner surface of the diesegment. The degree of inward contour is slight, and can be measured bythe maximum deviation, L_(D), from a straight line for a given outersurface length (L), i.e. L_(D)/L×100. In one aspect, the degree ofcontour can range from about 0.1% to about 2%; however, values outsidethis range can also be used. Specific ranges can be calculated based inthe die support member size, materials used in the support member, andnumber of force members used in a particular design. The degree ofcontour can be sufficient to distribute applied load such that hooptension at the die segments can be minimized. Those skilled in the artcan make such calculations using their knowledge and readily availablesoftware. When the die support member 110 of FIG. 8 is subjected to adiscrete force, the outer surface 114 tends to flatten with a largeportion of stress being transferred from the more expensive die segment112 to the support member.

Additionally, the die segment 112 can be shaped to reduce stress atcorners 116. For example, the corners can be rounded (as shown in FIG.8), tapered, or beveled. In this way, chipping or fracture of the diesegment at the corner can be reduced. Of course, in some embodiments,any gasket material used between die segments having shaped corners 116can be designed to match the contours of the contact surfaces 118.Preferably, the gasket material can be designed to eliminate orsubstantially fill any gaps between contact surfaces and/or the reactionassembly.

In yet another alternative embodiment of the present invention, thegasket material and corresponding contact surfaces of the die segmentscan be contoured to control pressure distribution through the assembleddie segments and to reduce premature failure. Under ultrahigh pressures,the pressure gradient from the inner surfaces of the die segments to theexterior surfaces of the die segments or supporting members can be verydramatic, i.e. typically from 1 atm (101,325 Pa) to 5.5 GPa. Generally,it is preferable to reduce sharp spikes or drops in pressure which causeadditional stress on die segments and support members. For example, thecontacting surface 118 can be flat with corresponding gasket materialshaving a constant thickness from the inner surface 120 of the diesegment to the outer surface 122 of the support member. In this case,the majority of the pressure drop occurs near the outer surfaceresulting in a large stress on the support member 110 in outer regionsnear the contact surface.

In order to produce a more uniform pressure gradient, the contactsurfaces 118 and corresponding gasket materials can be contoured. FIG. 9illustrates one embodiment wherein the contact surface is contouredoutwardly toward the inner surface 120 and the outer surface 124 with apeak at the interface between the support member 110 and the die segment112. The contact surface can be contoured with other configurations suchas gradual sloped surfaces or continuous taper, i.e. from the innersurface to the outer surface. For example, the gasket material can beshaped such that the gasket material is thicker toward the inner surfaceand tapers to a thinner thickness toward the outer surface.Alternatively, the gasket can have a thicker portion at the innersurface which then tapers to a narrower thickness near the joint betweenthe support member and the die segment at which point the thickness canremain substantially the same or taper either inward or outward. In eachof the above cases, the contact surfaces 118 can be contoured to matchthe gasket shape.

Further, in designing such contoured contact surfaces and correspondinggaskets a gradual decrease in pressure is desired. Typically, the slopeof the pressure change is related to the thickness of the gasket. Forexample, a thicker gasket can allow for a larger drop in pressure than athinner gasket. In addition, the difference between a thickest portionof the gasket and a thinnest portion of the gasket is typically verymoderate and can be less than about 3:1. Thus, by adjusting thethickness of the gasket material and the associated contact surfaces,the pressure gradient can be controlled to reduce mechanical stress atcertain portions of the die segment and/or support members.

The high pressure apparatus of the present invention can be used for avariety of high pressure applications. One suitable use of the apparatusof the present invention is high pressure growth of crystallinematerials such as diamond and CBN. Alternatively, the behavior andproperties of various materials can be studied at high pressures usingthe present invention.

For example, HPHT diamond synthesis typically involves formation of adiamond growth precursor. Typical precursors can include graphite powderand catalyst metal, i.e. a carbon solvent. Diamond seeds can also beincluded in order to control nucleation and growth of diamond. Aparticularly effective diamond growth precursor can have a controlledpattern of diamond seeds as described in U.S. Pat. No. 6,159,286, whichis incorporated herein by reference. The diamond growth precursor canthen be subjected to a temperature and pressure in which diamond isthermodynamically stable. As the temperature and pressure are increasedsufficiently to diamond growth conditions, the catalyst metalfacilitates formation of diamond from graphitic carbon. The growthconditions are maintained for a predetermined period of time to achievea specific size of grown diamond. Typical growth conditions can varysomewhat, however the temperature can be from about 1000° C. to about1600° C. and the pressure can be from about 2 to about 7 GPa, andpreferably from about 4 to about 6 GPa. The appropriate temperature candepend on the catalyst material chosen. As a general guideline, thetemperature can be from about 10° C. to about 200° C. above a meltingpoint of the catalyst. Growth time can typically be from about fiveminutes to about two hours.

Thus, there is disclosed an improved high pressure apparatus and methodsfor applying high pressure and ultrahigh pressure to materials. Theabove description and examples are intended only to illustrate certainpotential embodiments of this invention. It will be readily understoodby those skilled in the art that the present invention is susceptible ofa broad utility and applications. Many embodiments and adaptations ofthe present invention other than those herein described, as well as manyvariations, modifications and equivalent arrangements will be apparentfrom or reasonably suggested by the present invention and the foregoingdescription thereof without departing from the substance or scope of thepresent invention. Accordingly, while the present invention has beendescribed herein in detail in relation to its preferred embodiment, itis to be understood that this disclosure is only illustrative andexemplary of the present invention and is made merely for purpose ofproviding a full and enabling disclosure of the invention. The foregoingdisclosure is not intended or to be construed to limit the presentinvention or otherwise to exclude any such other embodiment,adaptations, variations, modifications and equivalent arrangements, thepresent invention being limited only by the claims appended hereto andthe equivalents thereof.

1. A high pressure apparatus, comprising: a) a plurality ofcomplementary die segments, each die segment having an inner surface andan outer surface, wherein the inner surfaces are configured to form adie chamber having a chamber axis upon assembly of the plurality of diesegments; b) a pair of anvils oriented such that an anvil is at each endof the die chamber and configured to apply force substantially along thechamber axis; and c) a plurality of force members operatively connectedto the plurality of die segments and configured to apply a plurality ofdiscrete forces to the plurality of die segments sufficient to retainthe plurality of die segments in substantially fixed positions relativeto each other during application of force by the pair of anvils.
 2. Theapparatus of claim 1, wherein the inner surfaces of the plurality of diesegments are arcuate and when assembled, form a die chamber having acentral cylindrical volume and expanded open conical regions at each endof the cylindrical volume.
 3. The apparatus of claim 2, comprising fromtwo to ten complementary die segments.
 4. The apparatus of claim 3,comprising two complementary die segments.
 5. The apparatus of claim 3,comprising four complementary die segments.
 6. The apparatus of claim 4,wherein the die chamber has a length of from about 1 to about 10 timesthe minimum diameter.
 7. The apparatus of claim 1, wherein the innersurfaces of the plurality of die segments are substantially flat andwhen assembled, form a die chamber having a central rectangular volumeand open regions tapered outwardly at each end of the rectangularvolume.
 8. The apparatus of claim 7, comprising four die segments. 9.The apparatus of claim 1, wherein the outer surfaces of the plurality ofdie segments are attached to a plurality of support members.
 10. Theapparatus of claim 9, wherein the force members are pairs of platen in auniaxial press and wherein a pair of support members are operativelyconnected to respective pairs of platen in each of at least one uniaxialpress.
 11. The apparatus of claim 10, wherein two die segments areattached to each support member.
 12. The apparatus of claim 9, whereinthe die segments and support members are integrally formed of a singlepiece.
 13. The apparatus of claim 9, wherein the plurality of supportmembers have an outer surface opposite the die segments, wherein theouter surface is inwardly contoured to form a profile configured toreduce tensile stress in the die segment.
 14. The apparatus of claim 9,wherein the die segments and support members have contoured contactsurfaces which are configured to control pressure distribution along thecontact surfaces and further comprises corresponding contoured gasketsconfigured for placement along the contact surfaces.
 15. The apparatusof claim 1, wherein the discrete forces intersect at a common point andact in a common plane substantially perpendicular to the chamber axis.16. The apparatus of claim 15, wherein the discrete forces are greaterthan the force applied by the pair of anvils.
 17. The apparatus of claim1, wherein the pair of anvils are frustoconical anvils.
 18. Theapparatus of claim 1, wherein the die chamber has a reaction volume fromabout 10 cm³ to about 500 cm³.
 19. The apparatus of claim 1, wherein thechamber axis is oriented horizontally.